全息再现的分析

从全息记录与再现技术的特点出发,对平面全息中的原始像、镜像、共轭像和共轭像的镜像的再现进行了分析,讨论了每个像再现的方法.     

Single-random-phase holographic encryption of images

In this paper, a method is proposed for encrypting an optical image onto a phase-only hologram, utilizing a single random phase mask as the private encryption key. The encryption process can be divided into 3 stages. First the source image to be encrypted is scaled in size, and pasted onto an arbitrary position in a larger global image. The remaining areas of the global image that are not occupied by the source image could be filled with randomly generated contents. As such, the global image as a whole is very different from the source image, but at the same time the visual quality of the source image is preserved. Second, a digital Fresnel hologram is generated from the new image, and converted into a phase-only hologram based on bi-directional error diffusion. In the final stage, a fixed random phase mask is added to the phase-only hologram as the private encryption key. In the decryption process, the global image together with the source image it contained, can be reconstructed from the phase-only hologram if it is overlaid with the correct decryption key. The proposed method is highly resistant to different forms of Plain-Text-Attacks, which are commonly used to deduce the encryption key in existing holographic encryption process. In addition, both the encryption and the decryption processes are simple and easy to implement.     

Label-free second-harmonic phase imaging of biological specimen by digital holographic microscopy

We have previously developed a new way for nonscanning second-harmonic generation (SHG) microscopy [Opt. Lett. 34, 2450 (2009)]. Based on digital holography, this technique captures, in single-shot hologram acquisition, both the amplitude and the phase of a coherent SHG radiation, which makes possible second harmonic phase microscopy. In this work, we present holographic SHG phase microscopy of a label-free biological tissue and discuss its added value to SHG microscopy.     

Quality of images decrypted from in-line holographic encryption of images

We investigate quality of images decrypted from in-line holograms recorded with a random phase mask placed behind an input image. High- and low-contrast fingerprint images are used as test scenes. The simulation results show that due to multiple convolution processes and a limitation of the CCD sensor resolution, quality of decrypted images is sensitive to spatial separations between the input image, the phase mask and the hologram. We propose a new method for improving quality of decrypted images by using background noise removal. It is found that in comparison with high-contrast input, the low-contrast image is more robust to distortion caused by the encryption–decryption process.     

New approaches in interpreting holographic images

This article presents an innovative system for interpreting holographic interferograms and other fringe patterns. The program is based on the phase-shift method of interpretation. Application of a special demodulation algorithm ensures extremely high reliability, while transputer technology is used at the same time to enable high-speed interpretation. The results are edited for user-friendly presentation and displayed in the form of pseudo-3D plots, profile images, false-color images, animate sequences, etc.     

Tomographic images improved by holographic synthesis

A holographic technique is used to combine the information content of conventional, 2D tomographic scan images into a full-parallax, 3D reconstruction of the recorded subject. Advantages of the system over the conventional, pseudo-3D reconstructions obtained by computer image processing, or over the direct examination of the scan images by the physician, are a more realistic and detailed information to the observer, as true parallax and physical depth cues are fully maintained.     

Resolution of holographic images of underwater objects

Interest is growing in the use of holographic visual inspection using real-image reconstruction as a means of making high resolution dimensional measurements on subsea components and structures. In this paper we report on the resolution obtained from holographic real images of targets in water filled observation tanks. These results indicate that measurements achieved in such circumstances can be superior to those obtained by stereo photogrammetry. A figure as high as 18 lp mm^-1 (line pairs per millimetre) has been obtained for a resolution target imaged through 300 mm of turbid water underlining the potential of the technique.     

Polychromatic reconstruction for volume holographic memory

We propose a method of reconstructing an image from a volume hologram at a wavelength different from the recording one. Spectrally broad but spatially coherent light was used as a probe beam. Each angular spectral component of the recorded hologram could be Bragg matched at one particular wavelength within the broadband spectrum. We experimentally demonstrated that a whole image could be reconstructed by using polychromatic light, whereas only a partial image was obtained by using single-mode laser light. We discuss the required bandwidth of the probe beam and the deformation of the reconstructed image.     

Subtraction via processing simultaneously recorded holographic images

The Fourier transform of two transparencies positioned centrally symmetric one with respect to the other, is recorded in the presence of a symmetric π/2 phase shifted reference beam. Illumination of the recorded hologram generates the subtracted image of the two inputs.     

Colour holographic images reconstructed by white-light processing

A method that uses white-light processing to reconstruct colour holographic images is introduced. Construction of the colour hologram and the optical arrangement for image retrieval are outlined. Advantages of the method are considered with reference to similar techniques such as reflection and rainbow holography.     

Quantum fluctuations in holographic teleportation of optical images

We investigate in detail the quantum fluctuations in the quantum holographic teleportation protocol that we recently proposed [11]. This protocol implements a continuous variable teleportation scheme that enables the transfer of the quantum state of spatially multimode electromagnetic fields, preserving their quantum correlations in space-time, and can be used to perform teleportation of 2D optical images. We derive a characteristic functional, which provides any arbitrary spatio-temporal correlation function of the teleported field, and calculate the fidelity of the teleportation scheme for multimode Gaussian input states. We show that for multimode light fields one has to distinguish between a global and a reduced fidelity. While the global fidelity tends to vanish for teleportation of fields with many degrees of freedom, the reduced fidelity can be made close to unity by choosing properly the number of essential degrees of freedom and the spatial bandwidth of the EPR beams used in the teleportation scheme.Received: 16 March 2004, Published online: 11 May 2004PACS: 03.67.-a Quantum information - 03.65.Bz Foundations, theory of measurement, miscellaneous theories (including Aharonov-Bohm effect, Bell inequalities, Berrys phase) - 42.50.Dv Nonclassical states of the electromagnetic field, including entangled photon states; quantum state engineering and measurements     

Expressions for third-order aberration theory for holographic images

Expressions for third-order aberration in the reconstructed wave front of point objects are established by Meier. But Smith, Neil Mohon, Sweatt independently reported that their results differ from that of Meier. We found that coefficients for spherical aberration, astigmatism, tally with Meier’s while coefficients for distortion and coma differ.     

高质量数字全息波面重建系统研究

基于阿贝成像理论对数字全息波面重建系统进行研究. 结果表明,利用成像系统对物光场进行变换,可以让物光场的高频角谱分量到达电荷耦合器件（CCD）探测器.为研究重建物光场质量,导出了CCD在光学系统后任意位置波面重建的计算公式,研究了物光通过傍轴光学系统到达CCD时波面重建系统的脉冲响应. 理论及实验研究表明,将CCD平面置于物光场像平面附近可以对物光场进行高质量重建. 关键词： 信息光学 数字全息 波面重建     

Determination of structure of weak scatterers from holographic images

For a weak scatterer a three dimensional Fourier transform of the image formed by a generalized hologram is shown to yield directly the Fourier transform of the scattering potential evaluated on the Ewald sphere. The entire scattering potential can be approximately determined if the object is illuminated from all directions in a series of experiments and if the scattering potential is essentially bandlimited to within a sphere of radius 4π/λ.     

全息照相实像的优化拍摄与再现

从全息照相的基本理论出发,分析了全息照相实像的产生条件,提出了用正入射平行光拍摄和再现全息照相实像的方案.实验表明,用正入射平行光拍摄和再现全息实像能得到满意的效果.在不同的散射介质中进行了全息实像的再现实验,确定了一种符合要求的再现介质.     

微细铣刀位姿同轴全息重建方法

微细铣刀在主轴上存在装夹偏角时,会加剧刀刃磨损,降低刀具使用寿命.为了精确观测微细铣刀在机倾斜状态,提出了基于景深的微细铣刀三维位姿重建方法.利用激光同轴数字全息实验装置得到微细铣刀全息图,并通过菲涅尔再现算法获得再现像.在再现像中提取刀具边缘点作为关键点,采用小波变换局部方差算子求出关键点的聚焦程度,确定铣刀对应的轴...     

Segmentation of holographic images using the level set method

Image segmentation, which is to distinguish objects from background, has played an important role in holographic image processing. In this work, we propose a technique that uses the combination of rough segmentation and the level set methods for segmentation of holographic images with zero-order diffraction interference. To improve the image quality, we eliminate the interference of zero-order diffraction in digital holography using Sobel differential gradient algorithm based on digital image processing. After reconstruction, the rough segmentation including intensity transformations and Morphology methods is applied to acquire the rough contour of the reconstruction image. Finally, we adopt level set methods to smooth the object contour and improve its accuracy. Segmentation results for objects in holographic images are presented.     

A new methodology for realizing magnification of holographic images

The article describes a new method for obtaining a holographic image of desired magnification, consistent with the stipulated criteria for its resolution and aberrations.